1. Field of the Invention
The present invention relates to microprocessor architecture in general and in particular to a microprocessor architecture capable of supporting multiple heterogeneous microprocessors.
2. Description of the Related Art
A computer system comprising a microprocessor architecture capable of supporting multiple processors typically comprises a memory, a memory system bus comprising data, address and control signal buses, an input/output I/O bus comprising data, address and control signal buses, a plurality of I/O devices and a plurality of microprocessors. The I/O devices may comprise, for example, a direct memory access (DMA) controller-processor, an ethernet chip, and various other I/O devices. The microprocessors may comprise, for example, a plurality of general purpose processors as well as special purpose processors. The processors are coupled to the memory by means of the memory system bus and to the I/O devices by means of the I/O bus.
To enable the processors to access the MAU and the I/O devices without conflict, it is necessary to provide a mechanism which assigns a priority to the processors and I/O devices. The priority scheme used may be a fixed priority scheme or a dynamic priority scheme which allows for changing priorities on the fly as system conditions change, or a combination of both schemes. It is also important to provide in such a mechanism a means for providing ready access to the memory and the I/O devices by all processors in a manner which provides for minimum memory and I/O device latency while at the same time providing for cache coherency. For example, repeated use of the system bus to access semaphores which are denied can significantly reduce system bus bandwidth. Separate processors cannot be allowed to read and write the same data unless precautions are taken to avoid problems with cache coherency.